Copy Part of Frame in 2D Animation Mode
You can copy part/s of a Grease Pencil object (Strokes and Points) as follows:
Copy/Paste

Go to the source Frame in the timeline
Ensure Blender is in Object Mode
Select your Grease Pencil Object
Change Blender to Edit Mode
Select the desired strokes/points/parts of the Object
Copy with: Ctrl-C  -or-  right-click Copy  -or-  [Grease Pencil] &gt; Copy
Change to the destination Frame in the timeline (new or existing)
Paste with: Ctrl-V  -or-  right-click Paste  -or-  [Grease Pencil] &gt; Paste
optionally Return to Object Mode (or continue editing)

You can also use similar techniques to copy parts of one Grease Pencil Object into another.
Duplicate
For Steps 5,6,7,8 - you can also use Duplicate (Shift-D) as follows:

Select the desired strokes/points/parts of the Object
Change to the destination Frame in the timeline (new or existing)
Duplicate with: Shift-D  -or-  right-click Duplicate -or-  [Grease Pencil] &gt; Duplicate
Hit [Enter] or left-click in the workspace to position the new duplicate

The Duplicate method has the effect of merging the Strokes and Points into whatever is currently visible in the destination frame.